Methods for producing enhanced interference pigments

ABSTRACT

Methods and apparatus are provided for uniformly depositing a coating material from a vaporization source onto a powdered substrate material to form a thin coalescence film of the coating material that smoothly replicates the surface microstructure of the substrate material. The coating material is uniformly deposited on the substrate material to form optical interference pigment particles. The thin film enhances the hiding power and color gamut of the substrate material. Physical vapor deposition process are used for depositing the film on the substrate material. The apparatus and systems employed in forming the coated particles utilize vibrating bed coaters, vibrating conveyor coaters, or coating towers. These allow the powdered substrate material to be uniformly exposed to the coating material vapor during the coating process.

CROSS-REFERENCE TO RELATED

This application is a continuation of U.S. patent application Ser. No.09/539,695, filed Mar. 31, 2000, now U.S. Pat. No. 6,524,831, andentitled “Methods for Producing Enhanced Interference Pigments” andclaims the benefit thereof.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention is related generally to thin film optical coatingsfor producing interference pigments. More specifically, the presentinvention is related to methods and apparatus for producing thininterference coatings in the form of thin coalescence films on pigmentparticles which exhibit enhanced colorant effects and hiding power.

2. The Relevant Technology

Interference pigments and colorants have been used to provide a coloredgloss in substances such as cosmetics, inks, coating materials,ornaments and ceramics. Typically, a silicatic material such as mica,talc or glass is coated with a material of high refractive index, suchas a metal oxide, and a layer of metal particles is further deposited ontop of such highly refractive material. Depending on the type and thecontent of the highly refractive material, different types of gloss andrefractive colors are produced.

Thin film flakes having a preselected single color have been previouslyproduced. For example, U.S. Pat. No. 4,434,010 discloses flakes composedof symmetrical layers that may be used in applications such asautomotive paints and the like. The flakes are formed by depositing asemi-opaque metal layer upon a flexible web, followed by a dielectriclayer, a metal reflecting layer, another dielectric layer, and finallyanother semi-opaque metal layer. The thin film layers are specificallyordered in a symmetric fashion such that the same intended color isachieved regardless of whether the flakes have one or the other lateralface directed towards the incident radiation.

High chroma interference platelets for use in paints, including colorshifting and nonshifting single color platelets, are disclosed in U.S.Pat. No. 5,571,624. These platelets are formed from a symmetricalmultilayer thin film structure in which a first semi-opaque layer suchas chromium is formed on a substrate, with a first dielectric layerformed on the first semi-opaque layer. An opaque reflecting metal layersuch as aluminum is formed on the first dielectric layer, followed by asecond dielectric layer of the same material and thickness as the firstdielectric layer. A second semi-opaque layer of the same material andthickness as the first semi-opaque layer is formed on the seconddielectric layer. For the color shifting designs, the dielectricmaterials utilized, such as magnesium fluoride, have an index ofrefraction less than 2.0. For small shifting or nonshifting designs, thedielectric materials typically have an index of refraction greater than2.0.

U.S. Pat. No. 5,116,664 discloses a pigment that is made by coating afirst layer of TiO₂ onto mica followed by coating the TiO₂ layer withpowder particles of at least one of the metals cobalt, nickel, copper,zinc, tin, gold, and silver. The metallic powder layer is deposited byan electroless wet chemical process to a thickness of 5 to 1000.Electron micrographs showed that these particles were in the form offinely divided rods.

U.S. Pat. No. 5,573,584 discloses a process for preparing forgery proofdocuments by printing with interference pigments. The pigments areformed by overcoating platelet-like silicatic substrates (micas, talc orglass flakes) with a first colorless or selectively absorbing metaloxide layer of high refractive index, a second non-selectively absorbingsemitransparent layer, and optionally, a third layer comprising acolorless or selectively absorbing metal oxide in combination withscattering pigments. The second non-selectively absorbingsemitransparent layer may be composed of carbon, a metal, or a metaloxide, which, for example, can be applied by gas phase decomposition ofvolatile compounds, such as compounds of iron, cobalt, nickel, chromium,molybdenum or tungsten, or metal oxides such as iron oxide, magnetite,nickel oxide, cobalt oxides, vanadium oxides, or mixtures thereof.

Overcoating of a base material such as a TiO₂-coated silicatic substratewith an outer layer of carbon, metal or metal oxide is usuallyaccomplished in conventional processes by chemical deposition methodssuch as electroless plating or pyrolysis methods. Electroless platingmethods involve a redox process with no extraction or supply of electriccurrent. Pyrolysis methods rely on the thermal decomposition of avolatile compound such as a hydrocarbon or an organometallic compoundwhose pyrolytic decomposition product is deposited on the surface to becoated.

Electroless deposition methods and pyrolytic methods, however, producelarge islands or dots of the material being deposited on the basematerial. Consequently, continuous coating is obtained at the expense ofdepositing enough coating material to sufficiently coat the gaps betweensuch large islands or dots. This extensive deposition leads in turn to athick coating which, because of its thickness, does not generate thebest chromatic colors. In short, these conventional methods producethick coalescence layers.

When the preservation of the surface structure of the material that isbeing coated is desired, a thick coalescence layer has thedisadvantageous feature of significantly altering such underlyingsurface structure. For example, photomicrographs of TiO₂-coated micathat were treated in an electroless cobalt plating bath have beenreported as showing finely divided rod-like particles on the surface ofthe TiO₂ layer. See, for example, U.S. Pat. No. 5,116,664, FIG. 1 andcol. 6, lines 10-16, showing and describing a coating with finelydivided rod-like particles.

Chemical methods of deposition and electroless plating methods aretypically limited to materials that involve hydrocarbons (liquid orgases), to organometallic compounds, and to metals, such as silver ornickel, that can readily be deposited by electroless processes. It isdesirable, however, to manufacture mica interference pigments withmethods that permit a much wider choice of materials. In particular, itis desirable to develop a process that can utilize materials, such asmetals and sub-oxides, that can be vacuum deposited, materials, such asmetal carbides, metal nitrides, metaloxynitrides, metal borides, andmetal sub-oxides, that can reactively be deposited in vacuum, andmaterials, such as diamond-like carbon and amorphous carbon, that can bedeposited by plasma-assisted vacuum methods.

Chemical methods of deposition and electroless plating methods typicallygenerate solutions that must be disposed of, and some of these methodsrely on catalytic substances that are incorporated into the pigments toan extent such that it prevents the use of the pigment in certainapplications in various consumer products such as cosmetics. To avoidthese problems and limitations, it is desirable to develop processes formanufacturing pigments that are more environmentally friendly and thatdo not rely on materials that can limit the use of the pigments. Inparticular, it is desirable to develop processes that reduce oreliminate the use of toxic materials and hazardous methods ofdeposition.

In addition to the need for developing processes for manufacturinginterference pigments that can use a great variety of materials, it isalso desirable to develop processes that can use cheaper materials andthat permit the production of highly adherent and hard films that do noteasily detach themselves from the substrate. In particular, it isdesirable to provide processes that use materials other than therelatively expensive and mostly toxic metal carbonyls that typicallyrequire an investment in equipment for handling them and for monitoringtheir use in specially confined facilities.

SUMMARY AND OBJECTS OF THE INVENTION

It is a primary object of the invention to provide methods and apparatusfor the production of thin interference coatings in the form of thincoalescence films on inorganic particles to form a pigment composition.

It is also an object of the invention to form thin coalescence filmswhich replicate the surface microstructure of the underlying substrateparticles without forming islands, rod-like or other agglomerates in thecoating that would structurally alter the underlying substrate surfacemicrostructure.

It is another object of the invention to provide pigment compositionsthat exhibit enhanced color effects and hiding power.

To achieve the foregoing objects, and in accordance with the inventionas embodied and broadly described herein, methods and apparatus areprovided for uniformly depositing a coating material from a vaporizationsource onto a powdered substrate material to form a thin coalescencelayer of the coating material that smoothly replicates the surfacemicrostructure of the substrate material. This is accomplished in a dryvacuum deposition process and in the absence of liquid solutions to forma powdered pigment composition.

In particular, uniform deposition of the coating material is achieved bydirecting an inorganic powdered substrate material into a vacuum chambercontaining a coating material vaporization source, and generating acoating material vapor from the coating material vaporization source ina dry vacuum process. The powdered substrate material is exposed to thecoating material vapor in a substantially uniform manner, and a thincoalescence film of one or more layers of a coating material is formedon the powdered substrate material that substantially replicates asurface microstructure of the powdered substrate material. The apparatusand systems employed in forming the coated particles utilize vibratingbed coaters, vibrating conveyor coaters, coating towers, and the like.These allow the powdered substrate material to be uniformly exposed tothe coating material vapor during the coating process.

A pigment composition produced by the method of the invention includes apowdered substrate material comprising a plurality of inorganic coreparticles having an observable surface microstructure. A coalescencefilm substantially surrounds the core particles of the substratematerial, and the coalescence film substantially replicates the surfacemicrostructure of the core particles. The pigment composition can becombined with various pigment media in order to produce a colorantcomposition for use in paints, inks, or plastics. In addition, thepigment particles can be optionally blended with other pigment flakes,particles, or dyes of different hues, chroma and brightness to achievethe color characteristics desired.

The pigment compositions of the present invention exhibit enhancedhiding power, enhanced chroma on a white background and enhancedselected chromas on a black background. These pigment compositions alsoexhibit a greater available color gamut. The hardness and good adherenceexhibited by the coalescence films on the pigment particles lead toadvantages such as durability and the absence of rub-off coating losses.

These and other objects, features, and advantages of the presentinvention will become more fully apparent from the following descriptionand appended claims, or may be learned by the practice of the inventionas set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the manner in which the above-recited and otheradvantages and objects of the invention are obtained, a more particulardescription of the invention briefly described above will be rendered byreference to specific embodiments thereof which are illustrated in theappended drawings. Understanding that these drawings depict only typicalembodiments of the invention and are not therefore to be consideredlimiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 shows a schematic cross-sectional view of an embodiment of thecoating apparatus of the invention that has a vibrating bed;

FIG. 2 shows a schematic cross-sectional view of an embodiment of thecoating apparatus of the invention that has a rotating drum coater;

FIG. 3A shows a schematic perspective view of an embodiment of thecoating apparatus of the invention that has an electromagnetic conveyorcoater;

FIG. 3B shows a side view of the electromagnetic conveyor coater that ispart of the embodiment shown in FIG. 3A;

FIG. 3C shows a top view of the embodiment shown in FIG. 3A;

FIG. 4A shows a schematic cross-sectional view of an embodiment of thecoating apparatus of the invention that has a free-fall tower;

FIG. 4B shows a square arrangement of coating material vaporizationsources;

FIG. 4C shows a hexagonal arrangement of coating material vaporizationsources;

FIG. 5A shows a schematic cross-sectional view of an embodiment of thecoating apparatus of the invention that has an oblique tower;

FIG. 5B shows a cross-sectional view of the device shown in FIG. 5A in aplane that is orthogonal to the longitudinal axis of the embodimentshown in FIG. 5A;

FIG. 6A is a scanning electron microscopic picture at 50000× of thesurface of Gold Pearl pigment prior to Cr-deposition according to theinvention;

FIG. 6B is a scanning electron microscopic picture at 50000× of thesurface of Cr-coated Gold Pearl pigment according to the invention;

FIG. 7A is a scanning electron microscopic picture at 75000× of thesurface of Super Green Pearl pigment prior to Cr-deposition according tothe invention;

FIG. 7B is a scanning electron microscopic picture at 75000× of thesurface of Cr-coated Super Green Pearl pigment according to theinvention;

FIG. 7C is a scanning electron microscopic picture at 100000× of thesurface of Cr-coated Super Green Pearl pigment according to theinvention;

FIG. 8 is a plot in a*b* color space showing the hue and chroma changesfor three pigments upon Cr-coating according to the invention;

FIG. 9 is a plot in a*b* color space of color coordinates for thepigment Violet Pearl on two background materials upon Cr-coatingaccording to the invention;

FIG. 10 is a plot in a*b* color space of color coordinates for thepigment Gold Pearl on two background materials upon Cr-coating accordingto the invention;

FIG. 11 is a plot in a*b* color space of color coordinates for thepigment Super Green Pearl on two background materials upon Cr-coatingaccording to the invention;

FIG. 12 is a plot in a*b* color space of color coordinates for thepigment Super Red Mearlin Luster on two background materials uponCr-coating according to the invention;

FIG. 13 is a plot in a*b* color space of color coordinates for thepigment Merck Iriodin® 221 Blue on two background materials uponCr-coating according to the invention;

FIG. 14 is a plot in a*b* color space of color coordinates for thepigment Irioding® 289 Flash Interference Blue on two backgroundmaterials upon Cr-coating according to the invention; and

FIG. 15 is a plot in a*b* color space of color coordinates for thepigment Iriodin® 299 Flash Interference Green on two backgroundmaterials upon Cr-coating according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to methods and apparatus for coating apowdered substrate material to produce optical interference pigmentcompositions with enhanced colorant effects. The methods and apparatusprovide for uniform deposition of a coating material from a vaporizationsource onto a powdered substrate material to form a thin coalescencefilm of the coating material. The thin coalescence film enhances thehiding power and color gamut of the pigment composition.

As discussed in greater detail below, physical vapor depositionprocesses are used for depositing a coating material to form a thincoalescence film on the powdered substrate material. The apparatusemployed in forming the coated particles utilize vibrating bed coaters,vibrating conveyor coaters, coating towers, or the like. These allow thepowdered substrate material to be uniformly exposed to the coatingmaterial vapor during the coating process. A coating materialvaporization source used in the deposition process can be selected froman evaporative source, a sputtering source, an electron beam depositionsource, an arc vapor deposition source, and the like.

Pigment Composition

The pigment composition produced by the methods and apparatus of theinvention includes a powdered substrate material comprising a pluralityof inorganic core particles having an observable surface microstructure.A thin coalescence film substantially surrounds the core particles ofthe substrate material such that the coalescence film substantiallyreplicates the surface microstructure of the core particles. The coatedparticles of the pigment composition generally have a single-layered ormulti-layered interior structure, with a thin continuous layer of thecoalescence film substantially surrounding each of the particles. Thepigment composition can be combined with various pigment media in orderto produce a colorant composition for use in paints, inks, or plastics.The colorant composition produces a predetermined optical responsethrough radiation incident on a surface coated with the colorantcomposition. The optical response includes enhanced color effects thatare due to the coating deposited on the substrate material according tothis invention.

The substrate material can be selected from a variety of particulatematerials such as various silicatic materials. Other suitable substratematerials include multilayer platelets such as MgF₂/Al/MgF₂ platelets,SiO₂/Al/SiO₂ platelets, and solgel-SiO₂/Al/SiO₂—solgel platelets,interference glass flakes (i.e., glass flakes having a defined thicknessin the range from about 0.2 μm to about 1 μm), and combinations thereof.The MgF₂, SiO₂, and solgel-SiO₂ layers on the aluminum cores of theabove platelets can have an optical thickness ranging from about 2quarter waves (qw) at about 400 nm to about 8 qw at about 700 nm. Thesubstrate material can be a particulate material, such as mica flakes,glass flakes, talc, boron nitride, and the like, which can be useduncoated, or precoated with a high refractive index material. The highrefractive index material is preferably a dielectric material with anindex of refraction of greater than about 1.65. Examples of suitablehigh refractive index dielectric materials include titanium dioxide,zirconium oxide, tin oxide, iron oxide, zinc oxide, tantalum pentoxide,magnesium oxide, tungsten trioxide, carbon, and combinations thereof.One preferred substrate material is a TiO₂-coated silicatic materialsuch as TiO₂-coated interference mica. The substrate materials describedherein can be used singly or in a variety of combinations as desired.

A variety of coating materials can be used to form the thin coalescencefilm on the substrate particles according to the present invention. Forexample, the coating material can include various light absorbingmaterials. Suitable coating materials include metals, sub-oxides such asmetal sub-oxides, oxides including metal oxides, nitrides such as metalnitrides and metaloxynitrides, borides such as metal borides, carbides,sulfides, carbon such as diamond-like carbon and other amorphous carbon(e.g., poco, graphite or vitreous) materials. Preferred coatingmaterials include gray metals and compounds thereof such as chromium,titanium, palladium, tin, nickel, cobalt, as well as other materialssuch as silicon, carbon, copper, and aluminum. Various combinations ofany of the above coating materials may also be utilized. More generally,coating material choice in this invention includes any material that canbe vacuum-deposited, reactively deposited in vacuum, or deposited inplasma assisted vacuum processes.

An absorber coating composed of a multilayer structure of two or morelayers can also be used. For example, in the chamber shown in FIGS.3A-3C (discussed in detail hereinafter), using alternate targets ofdifferent materials, an alloy or a material composed of extremely thinlayers can be deposited. In the case of an alloy, the alloy may formspontaneously or may simply be indistinguishable from a multilayeredabsorber layer since the coating thickness for each layer can be on theorder of about 5 Angstroms or less, and even less than about 1 Angstrom.As the substrate particles travel around the vibrating trays in thechamber, the particles are coated by a thin deposition from each sputtertarget. The particles not only experience movement under the target, butare agitated under each target as well by a particular vibrating tray.

Combinations of different absorber coating materials such as Ti/C, Pd/C,Zr/C, Nb/C, Al/C, Cu/C, TiW, TiNb, Ti/Si, Al/Si, Pd/Cu, Co/Ni, Cr/Ni,and the like, can be utilized to form a multilayer coating. Thesedifferent material combinations can each be deposited sequentially asalternating layers on the substrate particles so that the coalescentfilm on the particles is composed of multiple layers of two differentabsorber materials. Preferably, the different materials used together inthe coating each have a refractive index (n) and an absorptioncoefficient (k) that are approximately equal. Alternatively, threedifferent coating materials can be employed, or as many differentmaterials can be used as there are targets. Alloys can also be used ineach target for the coating, such as titanium silicide (TiSi₂),Hastelloys (e.g., Ni—Mo—Fe, Ni—Mo—Fe—Cr, Ni—Si—Cu), Monels (e.g.,Ni—Cu), Inconels (e.g., Ni—Cr—Fe), Nichromes (e.g., Ni—Cr), and variousstainless steels. Details regarding the properties of these and otheralloys can be found in the Chemical Engineers' Handbook, McGraw-Hill,2nd Ed., 2116 (1941), the disclosure of which is incorporated byreference herein.

One preferred embodiment of a coating material includes alternatinglayers of titanium and carbon (Ti/C) formed on particles of a substratematerial such as TiO₂-coated interference mica. The titanium layers areseparated by the carbon layers and each particle is encapsulated with afinal thin layer of carbon. The titanium and carbon layers aresequentially deposited from different targets at a thickness to provideabsorbing properties to the coating material. The number of layersdeposited depends on the thickness of the layers. For example, a largernumber of layers are formed for the coating material when each of thelayers are a few angstroms thick, whereas fewer layers are formed wheneach of the layers are many angstroms thick. Each of the layers oftitanium and carbon can have a thickness ranging from about 1 Å to about50 Å. Another preferred coating of alternating layers includes titaniumand silicon (Ti/Si), which can be formed in a similar manner as the Ti/Ccoating discussed above.

The sub-oxides prepared in the vacuum process are deposited either bydirectly evaporating the sub-oxide (e.g., TiO_(x), where x=1-1.9) or byreactively evaporating the metal in the presence of pure oxygen,moisture or air. The carbides are deposited by reactive evaporation ofmetals with hydrocarbon gas, such as methane. Borides are deposited byevaporation of metals in the presence of diborane or halogenatedborides, such as BF₃ (g). Nitrides are deposited in the presence ofnitrogen gas, and oxynitrides are deposited in the presence of gasmixtures, such as oxygen/nitrogen mixtures, air/nitrogen mixtures, andwater vapor/nitrogen mixtures. Ammonia may be substituted for thenitrogen if desired. Alternating layers of a metal and a nitride oroxynitride can be formed as the coating material such astitanium/titanium nitride, or titanium/titanium oxynitride.

The coating material is preferably deposited on the substrate particlesso as to form a thin coalescence film having a thickness from about 30 Åto about 150 Å, and preferably a thickness from about 60 Å to about 100Å. The exact thickness, however, depends strongly on the opticalproperties of the absorbing material.

The pigment composition of the invention can be combined with variouspigment media such as acrylic melamine, urethanes, polyesters, vinylresins, acrylates, methyl methacrylate, ABS resins, epoxies, styrenes,ink and paint formulations based on alkyd resins, and mixtures thereof.The pigment composition combined with the pigment media produces acolorant composition that can be used directly as a paint, ink, ormoldable plastic material. The colorant composition can also be utilizedas an additive to conventional paint, ink, or plastic materials.

In addition, the pigment composition can be optionally blended withvarious additive materials such as conventional pigment flakes,particles, or dyes of different hues, chroma and brightness to achievethe color characteristics desired. For example, the pigment compositioncan be mixed with other conventional pigments, either of theinterference type or noninterference type, to produce a range of othercolors. This preblended composition can then be dispersed into apolymeric medium such as a paint, ink, plastic or other polymericpigment vehicle for use in a conventional manner.

Examples of suitable additive materials that can be combined with thecoated particles of the invention include non-color shifting high chromaor high reflective platelets which produce unique color effects, such asMgF₂/Al/MgF₂ platelets or SiO₂/Al/SiO₂ platelets. Other suitableadditives that can be mixed with the pigment composition of theinvention include lamellar pigments such as aluminum flakes, graphiteflakes, glass flakes, iron oxide, boron nitride, mica flakes,interference based TiO₂ coated mica flakes, interference pigments basedon multiple coated platelike silicatic substrates, metal-dielectric orall dielectric interference pigments, and the like; and non-lamellarpigments such as aluminum powder, carbon black, ultramarine blue, cobaltbased pigments, organic pigments or dyes, rutile or spinel basedinorganic pigments, naturally occurring pigments, inorganic pigmentssuch as titanium dioxide, talc, china clay, and the like; as well asvarious mixtures thereof. For example, pigments such as aluminum powderor carbon black can be added to control lightness and other colorproperties.

The pigment composition of the invention can be easily and economicallyutilized in paints and inks for various applications to objects andpapers, such as motorized vehicles, currency and security documents,household appliances, architectural structures, flooring, fabrics,sporting goods, electronic packaging/housing, toys, product packaging,etc. The pigment composition can also be utilized in forming coloredplastic materials, coating compositions, extrusions, electrostaticcoatings, glass, and ceramic materials.

Vapor Deposition Methods

To produce coatings in the form of thin coalescence layers, theinvention relies on dry, physical vapor deposition methods and vacuumdeposition sources. The deposition methods produce very finedistributions of nucleation sites on the surface of the material to becoated, and in particular, the deposition methods utilized producecoalescence layers thin enough so as to minimally or negligibly alterthe structural features of the underlaying material surfacemicrostructure. The thin coalescence layers that can be obtained withsuch fine nucleation site distributions lead to comparatively thinnercoatings, with better chromatic colors.

In physical vapor deposition methods, the material to be deposited hasto be initially evaporated and deposition is subsequently accomplishedby depositing the evaporated material on a selected substrate. The lowtemperature vapor deposition methods utilized in the present inventionare all physical vapor deposition methods and include resistiveevaporation, electron beam deposition, cathodic arc evaporation, carbonrod arc evaporation, magnetron sputtering including both planar andhollow cathode, balanced and unbalanced sputtering, as well as radiofrequency sputtering.

In resistive evaporation the material is brought to the evaporationtemperature with the aid of a resistance source in an evaporativesource. Typically, an element made of a metal such as tungsten, tantalumor molybdenum holds the material to be evaporated and is heated bypassing an intense electric current through the element.

In electron beam deposition the material is heated by bombardment withhigh energy electrons until the material evaporates. This technique hasthe ability to concentrate a large amount of power in a small surfaceand it thus provides temperatures that are higher than the melting andevaporation points of refractory oxides and even refractory metals usedin resistive evaporation.

Arc vapor deposition uses a high intensity current, low voltage arc tovaporize a cathodic electrode (cathodic arc) or anodic electrode (anodicarc) and deposit the vaporized material on a substrate. Arcvaporization, especially cathodic arc evaporation, provides copiousamounts of film-ions and reactive gas ions.

The carbon rod arc evaporation differs from the above described cathodicarc evaporation in that the former operates in direct current (DC) modewhile the latter operates in alternating current (AC) mode. The carbonrods are forced together to form an electrical short which causes highcarbon temperature in the contact area, and therefore evaporation.

Sputtering is ejection by bombardment and sputter deposition is anon-thermal process where the atoms of the material to be evaporated areejected upon energetic collision with impinging particles that aretypically inert gaseous ions and more particularly argon cations. Theinert gas ions are formed by ionizing collisions with electrons in avacuum chamber and they are accelerated by an electric potential towardsthe material to be sputtered. The material that is evaporated bysputtering subsequently deposits on a substrate.

According to a basic sputtering technique, a sputtering cathode and ananode are enclosed in a chamber that contains rarefied inert gas. Theseelectrodes are connected to a high voltage DC power supply whichaccelerates electrons to the anode. Electrons collide with the inert gasto form inert gas anions that accelerate to the cathode. The anionscollide with the sputtering cathode material and vaporize the materialthat is subsequently deposited on a substrate interposed between thesputtering cathode and the anode. This is DC sputtering or moreprecisely DC diode cathodic sputtering, which typically operates atpressures in the order of 10⁻² Torr.

The ion formation rate in a sputtering chamber can be enhanced byproviding electrons from, for example, a source such as a heatedfilament. The electrons are accelerated by a discharge DC power supply.This enhancement in the electron generation rate leads to an increase inthe deposition rate, and systems that operate according to thisprinciple are known as triode sputtering systems.

A sputtering system that, instead of a high voltage DC power supply, hasa radio frequency (RF) power supply and a matching chamber is a RFsputtering system. This system prevents the charge build-up in anonconducting material that is to be sputtered and it consequentlypermits the sputtering of insulating materials, typically beingperformed at pressures of an order of magnitude as low as 10⁻⁴ Torr.

Deposition rates achieved with radio frequency sputtering systems can befurther increased with magnetron sputtering. As in the previouslyintroduced sputtering techniques, a plasma exists in the sputteringchamber of a magnetron sputtering device, but appropriately generatedmagnetic fields additionally force the electrons to follow paths in theregion near the sputtering cathode. Accordingly, the frequency ofcollisions with inert gas atoms is higher and more sputtering ions areformed. The progressive increase in sputtering and deposition rates isalso characterized by a correspondingly increased ability to perform thedeposition at lower pressures.

In ion beam sputtering an ion source provides a focused, divergent orcollimated ion beam. The ion beam, in the form of a beam plasma, isdirected against a sputtering target and the sputtered atoms aredeposited on a substrate.

Reactive sputtering is a sputtering process in which a gas is introducedinto the chamber so it reacts with the evaporated material to form acompound that is deposited on the substrate. Even when a compound issputtered directly, the addition of a reactive gas may be necessary tocompensate for the dissociation losses of the reactive component.

Although reactive sputtering can arguably be classified as a chemicalvapor deposition method, reactive methods used in this invention rely onvacuum deposition sources that are used in physical vapor depositionmethods. In this sense, the reactive deposition methods of thisinvention are referred to in this context as physical vapor depositionmethods.

Sputtering can be carried out by using “balanced” or “unbalanced”magnetic field confinement. “Balanced” magnetron or “standard”sputtering occurs when most of the magnetic field lines are confined tothe target region. Unbalanced sputtering occurs when an externalmagnetic field is placed behind the substrate, or the magnets behind thesputtered target are of different strengths so that the ion and electronflux extends out away from the target toward the substrate. Generally,unbalanced magnetron sputtering rates are higher than for “balanced”magnetron sputtering with higher ion fluxes. Higher fluxes modify thegrowing deposited film to produce such changes as harder films withdiffering optical properties. A good review of the difference between“balanced” and “unbalanced” magnetron sputtering can be found in thefollowing references which are incorporated herein by reference in theirentirety: B. Window and N. Savvides, J. Vac. Sci. Technol. Vol. A4(2)196 (1986); and N. Savvides and B. Window, J. Vac. Sci. Technol. Vol.A4(3) 504 (1986).

Sources of electrons that are used for heating and ionizing atoms andmolecules include hot electron emitting surfaces and plasma sources. Inplasma sources, electrons are magnetically deflected from a plasma. Inparticular, the hollow cathode electron source uses a plasma dischargein a cavity that reflects and traps electrons.

These and other deposition techniques have been described in R. Herrmannand G. Bräuer, DC and RF-Magnetron Sputtering, and J. Becker, Ion BeamSputtering, in Handbook of Optical Properties, vol. 1, pp. 135-212, R.E. Hummel and K. H. Guenter (eds.), CRC Press (1995), which areincorporated by reference herein in their entirety.

In alternating current magnetron sputtering, e.g., “dual magnetronsputtering”, the voltage between two sputter sources is alternated tofacilitate the continuous sputtering of conductors that developinsulating layers in reactive sputtering. In this mode of deposition, areactive gas such as oxygen, nitrogen, methane, and ethylene isintroduced near the substrate surface in addition to the noble workinggas (e.g., argon). By alternating the targets between cathodic andanodic charge, both targets remain free of insulating reactants.

The MetaMode™ process developed by Optical Coating Laboratory, Inc.,(U.S. Pat. Nos. 4,851,095 and 5,225,057, which are incorporated hereinby reference in their entirety), allows continuous sputtering of ametallic target where a reactive process takes place in anothercontiguous chamber. Such a process is useful in making TiO_(x) orSiO_(x) absorbing layers from Ti metal or Si metal depositions.

The use of an ion gun to bombard the surface of the growing absorberfilm with ions is applicable to this invention since many films needhardening to prevent the outer layer from abrading off during milling ofthe pigment or application (compounding in plastics or painting) to thefinal product. In addition charge build-up on the powders duringdeposition could be reduced by the application of such ions. Variousmeans to coat such powders by ion assisted processes include ionplating, and reactive ion plating and are well known to those skilled inthe art.

Vapor Deposition Systems and Apparatus

The coating apparatus of this invention includes a substrate exposuredevice. The substrate exposure device is configured such that thesubstrate particles are uniformly exposed to the coating material duringthe coating process. An exemplary embodiment of a substrate exposuredevice is a vibrating bed that has a sample receptacle, such as a pan,that is connected to a vibrating device, such as a toroidalelectromagnetic vibrator. Additional exemplary embodiments of substrateexposure devices are vibrating conveyors, rotating drum coaters,oscillatory drum coaters, and free-fall chambers.

In some embodiments of this invention, the substrate exposure device islocated within a rarefied chamber (hereinafter referred to as “vacuumchamber”). For example, the vibrating beds, vibrating conveyors (e.g.,electromagnetic or pulsating gas-driven devices), rotating drum coatersand oscillatory drum coaters are located within a vacuum chamber. Inother embodiments of this invention, the substrate exposure deviceitself serves as the chamber whose interior is subject to rarefactionduring deposition. For example, “waterfall-equipped” chambers andfree-fall chambers are embodiments of substrate exposure devices thatserve themselves as vacuum chambers.

In embodiments of the substrate exposure device of this invention, theparticles of the substrate material are exposed to a vacuum depositionsource, such as a hollow cathode sputtering system or a DC magnetronsputtering system. For example, a DC magnetron sputter target ofchromium was used to deposit a uniform layer of chromium over thesurfaces of interference mica. Visual inspection revealed that theappearance of the particles went from a pale white to a visual color,and turned gray with further deposition, gray being the color ofelemental chromium. Too much chromium coating resulted in the depositionlayer being too thick and the coating was opaque. As long as thechromium layer was still semi-opaque (partially transmitting), enhancedcolor could be achieved as well as higher hiding. When the substrate wassubject to vibration while being exposed in an embodiment of thesubstrate exposure device, the pigment could be significantly improvedin color by adjusting the degree of vibration, the time of deposition,the power to the sputter target, the throw distance, and the amount ofsubstrate pigment being coated.

In addition to a substrate exposure device, embodiments of the coatingapparatus of this invention also have a vacuum deposition source as acoating material vaporization source. Exemplary configurations of theseelements are illustrated by the embodiments disclosed hereinbelow.

Any of the embodiments of the coating apparatus of this invention hereindisclosed provides effective and uniform exposure of the substratematerial powder. This means that statistically all the sides of thesubstrate material powder particles are approximately equally exposed tothe coating material that is to be deposited on them. This type ofexposure is hereinafter referred to as “uniform exposure”.

FIG. 1 schematically shows a vertical cross-sectional view of a coatingapparatus 100 according to one embodiment of the invention, in which avacuum chamber 110 encloses a coating material vaporization source 120and the substrate exposure device that is embodied by a vibrating bed130. A powdered substrate material 132, such as TiO₂-coated mica, isplaced in a rotatable container 134, which is operatively connected to avibrator 140. In one embodiment, container 134 is located on andattached to a base 135 by a conventional fastener 136. In otherembodiments, base 135 is integrally attached to container 134, or base135 forms the base of container 134 itself. Container 134 is moreparticularly embodied by any receptacle that can effectively holdsubstrate material 132 while it is being coated, such as a bowl-shapedcontainer, a dish or a pan.

The vibrator 140 comprises a vacuum sealed electromagnet 142. In thisembodiment, base 135 is made of a magnetic material, preferably magneticsteel. Furthermore, flat springs 144 connect base 135 with the bottom ofelectromagnet 142 or with a fixed surface 146 so that base 135 isprevented from contact engagement with electromagnet 142, and base 135can move without experiencing collisions against any other part ofelectromagnet 142. During operation of coating apparatus 100, substratematerial 132 undergoes a substantially helical motion that isrepresented in FIG. 1 by arrows A1 and A2. This continuous mixing ofsubstrate material 132 in container 134 provides for a good statisticaldistribution of the thickness of the deposited coating on the substratematerial.

The coating material is vaporized from coating material vaporizationsource 120, which in one embodiment of this invention is an evaporativesource. In other embodiments of this invention coating materialvaporization source 120 is a magnetron sputtering unit or any of thevacuum deposition sources described hereinabove. As depicted in FIG. 1,a flow 152 of vaporized coating material emanates from coating materialvaporization source 120 to reach and coat substrate material 132.

When electromagnet 142 was operated in the approximate voltage range of0-50 V at 60 Hz, it generated an alternating magnetic field thatsuccessively attracted and released base 135 at a frequency of 60 Hz,thus causing partially circular up-and-down oscillations of bowl-shapedcontainer 134. When electromagnet 142 was turned on, an alternatingmagnetic field attracted base 135 to the top of electromagnet 142 andreleased it with the frequency of 60 Hz. Flat springs 144 did not letbase 135 contact the top of electromagnet 142 and returned base 135 tothe original position every time when the field changed its polarity.With these oscillations imparted to container 134, substrate material132 was continuously mixed and effectively and uniformly exposed to thevaporized material that deposited on the surface of the particles ofsubstrate material 132.

The appropriately rarefied environment in the chamber where depositiontakes place in the embodiment schematically shown in FIG. 1 or in anyother embodiment disclosed hereinbelow is achieved with the aid ofconventional vacuum pumping systems. These systems typically include acryopump, a diffusion pump coupled to a mechanical pump or othersuitable vacuum pump, or combinations thereof, with the suitable vacuumlines and exhaust ports. These systems are known to those skilled invacuum technology and are not further discussed here.

In preferred embodiments, the size of the vibrator bowl can range from 4inches to about one foot in diameter. The vibrator should be soconstructed that little outgassing occurs from its components, andpreferably, stainless steel is used in its construction. Embodiments ofcoating material vaporization source 120 (also referred to as sputteringtarget or simply target) may be any shape including annular orrectangular. A preferred embodiment for chromium deposition comprises awater cooled DC magnetron with a chromium target having dimensions of 12inches by 4.4 inches by 0.50 inches thick. Annular targets having radiifrom about 4-9 inches could be used as well as larger rectangulartargets up to about 11 inches by about 4 feet long. By using multiplecathodes arranged in a square with multiple vibrating bowls, largevolumes (about 5 pounds) of pigment can be produced in one batchoperation. In an embodiment with a small 4-inch radius vibrator bowl andone overhead coating material vaporization source, about 10 grams ofpigment could be effectively processed.

FIG. 2 schematically shows a vertical cross-sectional view of a coatingapparatus 200 according to another embodiment of the invention, in whicha vacuum chamber 210 encloses a coating material vaporization source 220and the substrate exposure device that is embodied by a rotating drumcoater 230. A substrate material 232, such as TiO₂-coated mica, isplaced in a hollow drum 233 which is rotated as indicated, for example,by arrow A3 under the power delivered at a chosen angular frequency by ashaft 234. The interior wall 235 of drum 233 is so manufactured as toprovide for the effective mixing and uniform exposure of substratematerial 232.

A plurality of ledges 238 extend generally inwards from interior wall235 of drum 233 so that, upon revolving drum 233, ledges 238 lift acertain amount of the powder of substrate material 232. As drum 233continues turning, the powder of substrate material 232 falls backdownwards thus undergoing the efficient mixing that leads to uniformexposure and subsequent deposition of coating material. The ledges 238are arranged so that the powder of substrate material 232 preferablyfalls back in such a way that most of the powder is effectively exposedto the flow of coating material. For example, in the arrangementdepicted in FIG. 2, this is accomplished by forcing the powder to fallback shortly after each ledge has passed the relevant equatorial zone ofthe drum, forcing the powder to undergo a motion schematically indicatedby arrow A4. The ledges 238 are arranged differently in otherconfigurations so as to provide the desired uniform exposure of thepowder of substrate material 232 depending on how and where coatingmaterial vaporization source 220 is located within vacuum chamber 210.Furthermore, other features that accomplish an equivalent result can beused instead of ledges 238, such as flanges, bars, paddles, and blades.

The coating material is vaporized form coating material vaporizationsource 220, which in one embodiment of this invention is a physicalevaporative source. In other embodiments of this invention coatingmaterial vaporization source 220 is a magnetron sputtering unit or anyof the vacuum deposition sources described hereinabove. As depicted inFIG. 2, a flow 252 of vaporized coating material emanates from coatingmaterial vaporization source 220 to coat substrate material 232.

The drum coater 230 is a preferred exemplary embodiment of a coater ofthis invention that is in other embodiments shaped like a generallyrotary cylindrical coater, or in general like a rotary container that issuited for mixing the powder of substrate material 232 and exposing itto vaporized coating material.

The rotating drum coater has been described previously. Teer, inReactive Magnetron Sputter Barrel Ion Plating, as reported in ConferenceProceedings IPAT 91, pp. 303-308, Brussels, Belgium, which isincorporated herein by reference in its entirety, shows a typical drumor barrel coater in FIGS. 1-3 which has a diameter of about 2 feet.However, there are physical constraints in making a bigger chamber, suchas a chamber 6 feet in diameter. The two-foot chamber used was equippedwith a sputtering system in which the deposition occurred downward onpowder flowing across the bottom inside of the rotating drum. Theinterior of the barrel was provided with angled bars which allowed thepigment to be agitated uniformly and not lost to the ends of the barrel.

FIG. 3A schematically shows a perspective view of a coating apparatus300 according to a further embodiment of the invention, in which avacuum chamber 310 encloses both a coating material vaporization source320 and the substrate exposure device, which is embodied by a vibratingconveyor coater 330. As shown in FIG. 3A, vibrating conveyor coater 330preferably has four conveyors 371, 372, 373, and 374 which are disposedso that the powder of a substrate material 332 effectively circulatescounterclockwise as indicated by arrows A5. While the powder circulatesalong this path, it is effectively mixed so that its exposure to thevaporized coating material is uniform. Efficient mixing also occurs atthe end of each conveyor as the powder drops in a waterfall off of onetray and onto the next. The vaporized coating material is provided bycoating material vaporization source 320, which in one embodiment ofthis invention is a physical evaporative source. In other embodiments ofthis invention coating material vaporization source 320 is a magnetronsputtering unit or any of the vacuum deposition sources describedhereinabove.

A vibrating means is provided to force the powder of the substratematerial 332 to circulate. For example, in one embodiment, vibratingconveyor coater 330 can be associated with a plurality of electromagnets342 which act as the vibrating means. FIG. 3B schematically shows a sideview of conveyor coater 330, and in particular, the components of theelectromagnetic conveyors which include a tray 334, a shaft 335, anelectromagnet 342, and a spring 344. The tray 334 can be made of avariety of materials, and preferably is made of stainless steel. Asindicated in FIG. 3B, tray 334 is longitudinally tilted with respect tothe horizontal plane by an angle that is preferably between about 1° andabout 20°, and more preferably between about 1° and about 5°. In thisarrangement, electromagnet 342 is located near a lower end 337 of tray334 and preferably under such lower end. A higher end 339 of tray 334 ispreferably cut as shown in FIG. 3C, preferably at an angle of about 45°with respect to the longitudinal axis of tray 334. One end of spring 344is preferably attached to electromagnet 342 and its opposite end isattached at a point near lower end 337 of tray 334. Similarly, one endof shaft 335 is attached to electromagnet 342 and the opposite end isattached preferably to a region under tray 334 that is located betweenthe half-length point of tray 334 and lower end 337. Furthermore, shaft335 is conventionally attached to electromagnet 342 to effectively forcetray 334 to oscillate according to corresponding oscillations generatedby electromagnet 342. The restoring effect of spring 344 effectivelycreates a torque that tends to restore tray 334 to the position that ithad prior to the displacement caused by electromagnet 342 acting uponshaft 335. The overall dynamic behavior of tray 334 coupled with spring344 and shaft 335 is such that the powder of substrate material 332 iseffectively forced upwards from lower end 337 to higher end 339 alongtray 334.

In other embodiments of the vibrating conveyor coater of the presentinvention, the vibrating tray can be energized by other vibrating meanssuch as a pulsating gas-driven device. For example, a pulsating airpiston known as a pneumatic drive, attached to the vibrating tray, canbe used to induce the vibrating motion in the tray. Such pneumatic drivesystems are available from Martin Engineering (Livonia, Mich.).

Each one of trays 334 in the embodiment schematically shown in FIG. 3Ais disposed so that each higher end 339 is located above lower end 337of the next tray along the overall circulation path of substratematerial 332. This arrangement is shown in the perspective view of FIG.3A and in the side view of FIG. 3B. When conveyor coater 330 has fourconveyors, they are disposed with respect to each other in the abovedescribed configuration at preferably about 90° angles, as shown in theperspective view of FIG. 3A and in the top view of FIG. 3C.

FIG. 3B shows tray 334 lengthwise and also shows an end view of thefollowing tray, electromagnet and spring in the sense of circulation ofsubstrate material 332. Primed and unprimed numbers in FIG. 3B labelanalogous elements in the lengthwise view and in the end view,respectively.

FIG. 3C shows a top view of the embodiment shown in FIG. 3A, wheredifferently shaded areas represent different trays 334 of differentconveyors 371-374 forming a closed-loop square array. As schematicallyshown in FIG. 3C, the powder of substrate material 332 is forced to moveby the vibration of tray 334 along conveyor 371, and is coated with thevaporized coating material from coating material vaporization source320. The coated powder then drops off at the higher end 339 of conveyor371 onto lower end 337 of conveyor 372. Consequently, the powder movesalong the path indicated by arrows A5. The overall powder flow changestravel direction by approximately 90° when it is dropped from oneconveyor to the next conveyor along the path. In addition, the powderfalls several inches when it is delivered from one conveyor to thefollowing conveyor so that the powder is thoroughly mixed to provideuniform exposure to the vapor of the coating material that is to depositon and coat substrate material 332. The approximately 45° cut at thehigher end 339 of each tray 334 permits a uniform fall of the powderonto the entire width of the lower end 337 of the following tray.

The counterclockwise overall circulation of substrate material 332 asshown in FIGS. 3A and 3C is merely illustrative of one possiblecirculation in an embodiment of this invention. Modifications to thedevices shown in FIGS. 3A, 3B and 3C could be made by one of ordinaryskill in the art to produce another embodiment of this invention inwhich the overall circulation of substrate material 332 is clockwise.

In a typical embodiment of the vibrating conveyor coater, traydimensions are about 28 inches long by about 7 inches wide, althoughcommercially available conveyors come in lengths up to 30 feet andwidths up to 2 feet. Multiple two-foot wide sputter targets would allowdeposition through the length of the larger vibrating trays. Instead ofa square arrangement, embodiments of this device could have triangulartray arrangements, pentagonal arrangements, hexagonal arrangements, orarrangements in some other shape. Still another embodiment of thisdevice could have a long vibrating tray with multiple overheadevaporating sources. Vibrating conveyors of this type are available fromARBO Engineering (North York, Ontario, Canada) and Eriez (Erie, Pa.).The preferred arrangement is the square arrangement of vibrating trayswith four waterfalls at each 90° turn.

FIG. 4A schematically shows a vertical cut-away view of a coatingapparatus 400 according to another embodiment of the invention, in whichthe vacuum chamber comprises a tall and narrow elongated coating towerstructure such as a free-fall tower 405 with a series of mounted coatingmaterial vaporization sources 420 and a container 450 for a substratematerial 432. The tower 405 is provided with a receptacle 434 to collectand facilitate the subsequent retrieval of a coated substrate material433.

In one embodiment of coating apparatus 400, coating materialvaporization sources 420 are magnetrons. In another embodiment, coatingmaterial vaporization sources 420 are hollow cathode sputtering systems.

When magnetrons are utilized for vaporization sources 420, themagnetrons can be mounted in a variety of configurations, but preferablythey are mounted in a square or hexagonal configuration, as shown inFIGS. 4B and 4C. These figures schematically illustrate cross-sectionalviews of coating apparatus 400 taken in a plane that is orthogonal tothe tower's longitudinal axis. FIG. 4B shows a cross-sectional view of asquare tower 406 with four magnetrons 421. FIG. 4C shows an analogouscross-sectional view of a hexagonal tower 407 with six magnetrons 422.Square and hexagonal shaded regions 425 and 426 schematically illustratethe region into which the plasma in towers 406 and 407, respectively, isconfined by the magnetic fields of the corresponding magnetrons 421 and422. In general, magnetrons are preferably installed over all sides ofthe coating tower to increase the deposition rate of the coatingmaterial onto the powder particles of substrate material 432.

The container 450 is provided with a mechanism for appropriatelyreleasing substrate material 432 into tower 405. In the embodimentillustrated in FIG. 4A, this mechanism is exemplary embodied by apercussion mechanism such as a hammer 452 that, as indicated by doublearrow A6, forces the release of substrate material 432 by appropriatelyshaking container 450. This can also be achieved by any other mechanismthat produces a similar effect, such as a vibrator.

As schematically shown in FIG. 4A, after substrate material 432 has beenreleased from container 450, substrate material 432 falls down through aseries of plasma regions 427 and past coating material vaporizationsources 420. Because of convection and plasma forces, the powderparticles spiral down to the bottom where they are collected inreceptacle 434. The movement of the powder particles during fall allowsfor uniform exposure and deposition of a coating material thereon.

FIG. 5A schematically shows a vertical cross-sectional view of a coatingapparatus 500 according to an additional embodiment of the invention, inwhich the vacuum chamber comprises a tall and narrow oblique coatingtower 505 with a series of mounted coating material vaporization sources520 and a container 550 for a substrate material 532. The tower 505 isprovided with a receptacle 534 to collect and facilitate the subsequentretrieval of a coated substrate material 533. In one embodiment, coatingmaterial vaporization sources 520 are magnetrons.

The tower 505 stands at an angle preferably in the range of about70°-89° relative to a horizontal plane intersecting the longitudinalaxis of tower 505. Equivalently, tower 505 stands at an angle preferablyin the range of about 1°-20° relative to a vertical axis, as shown inFIG. 5A.

Coating material vaporization sources 520, such as magnetrons, aremounted on one wall of tower 505. Within tower 505, a device isgenerally disposed along the wall opposite vaporization sources 520 toforce particles of substrate material 532 to undergo a motion such thatit renders them fully and uniformly exposed to the coating material thatemanates from vaporization sources 520. In one embodiment, this deviceis a vibrating tray 508 with ledges that is longitudinally disposedalong the wall opposite vaporization sources 520. In another embodiment,this device is a stationary tray with ledges that is generally disposedas tray 508.

FIG. 5B schematically shows a cross-sectional view of coating apparatus500 in a plane that is orthogonal to the longitudinal axis. As shown inFIG. 5B, tray 508 is provided with longitudinally extending lateralflanges 509 that confine the particles as they run downward over theledges of tray 508.

During operation of coating apparatus 500, a mechanism such as avibrator or a similar device forces substrate material 532 to bereleased from container 550 and to fall down on tray 508. Particles ofsubstrate material 532 slide along the ledges of tray 508, flipping andmixing, and pass through a series of plasma regions 527. The particlesare uniformly exposed and coated with the coating material that emanatesfrom coating material vaporization sources 520, resulting in coatedsubstrate material 533 which is collected in receptacle 534.

Preferred embodiments of the towers schematically shown in FIGS. 4A and5A are typically about 3 feet in diameter and about 6 feet long. Theseembodiments also include (not shown in FIGS. 4A-5A) a return mechanismto the top of the tower for further processing of the pigment, ifnecessary. The pigment is circulated through the tower as many times asnecessary until the desired color is achieved. The return mechanism canbe embodied by a screw conveyor, a spiral vibrating elevator, or by aferris wheel arrangement to reload the powder at container 450 or 550from the respective receptacle 434 or 534. The sputter targets are ofsuitable dimensions to fit within the chambers.

Elements of the embodiments of the coating apparatus of this inventiondescribed hereinabove, equivalents thereof, and their functionalitiescan be expressed as means for performing specified functions asdescribed hereinbelow.

Examples of means for directing an inorganic powdered substrate materialinto a vacuum chamber include any of a variety of conventional conveyingdevices known to those skilled in the art of vacuum depositionprocessing.

Examples of means for generating a coating material vapor include anyone of a plurality of coating material vaporization sources such assputtering sources including sputter magnetrons, hollow cathodesputtering systems, triode sputtering systems, RF sputtering systems,ion beam sputtering sources, hollow cathode sputtering systems, andreactive sputtering sources; evaporative sources; electron beamdeposition sources, and arc vapor deposition sources including cathodicarc vapor deposition sources and anodic arc vapor deposition sources, aswell as carbon rod arc evaporation.

Examples of means for uniformly exposing powdered substrate materialinclude any of a plurality of substrate exposure devices that uniformlyexpose substrate material powder in a rarefied environment to coatingmaterial vapor, such as vibrating beds and conveyors, rotating drumcoaters, electromagnetic conveyor coaters, and coating towers includingstraight and oblique towers.

Examples of a means for providing a rarefied environment for vapordeposition include any one of a variety of vacuum pumping systemsincluding cryopumps, other vacuum pumps and combinations thereof, withthe appropriate vacuum lines and exhaust ports.

Feeding mechanisms such as a container coupled to a percussion device orto a vibrator are examples of means for supplying powdered substratematerial. These mechanisms and equivalents thereof supply powdersubstrate material to means for uniformly exposing substrate materialpowder. Containing devices such as a receptacle are examples of meansfor collecting coated substrate material powder. Feeding mechanisms andequivalents thereof, and containing devices and equivalents thereof areappropriately placed so that they do not interfere with the uniformexposure of the substrate material powder to the coating material vapor,so that they do not impede the deposition of the coating material vaporonto the substrate material powder, and so that the rarefied conditionsin which the vapor deposition takes place are preserved.

Thin Coalescence Layer Coatings

The structure of the coated particles of the pigment composition of theinvention, particularly when the coating material is a metal, ismarkedly different from the structure of the pigments produced accordingto conventional methods. Electroless deposition and pyrolyticdecomposition methods for organometallic compounds produce large islandsor dots of metal. If these deposition methods are prolonged to induce acontinuous coating, the absorber coating becomes too thick atcoalescence to produce the best chromatic colors. In contrast, thephysical vapor deposition processes of this invention produce a veryfine distribution of nucleation sites on the surface of the substratematerial, such as the surface of TiO₂-coated mica, which in turn producea very thin coalescence thickness.

In this invention, the coating is not composed of dot-like or rod-likeformations, and the continuous covering is achieved at a much thinnercoverage than with other methods, such as electroless or chemical vapordeposition processes. Metals and other materials deposited by physicalvacuum processes according to the invention can have a thickness ofabout 30-150 Å, and coalesce at thicknesses that are as small as about30-50 Å. For example, a coalescence thickness of about 40 Å was commonlyachieved in the experiments performed in the context of this invention.

Deposition according to this invention is supplemented in someembodiments with a process for altering the chemical makeup of thedeposited material. In one embodiment of this invention, the depositedmaterial is oxidized, forming a somewhat thicker layer that increasesthe durability of the final pigment. For example, the pigment productcan be baked after vacuum deposition to produce a thicker oxide layer,since a metal layer would be oxidized somewhat after the heatingprocess. The thickness of the layers of deposited material that areobtained in this way can be up to about 200 Å while still replicatingthe underlying structure of the material on which deposition takesplace.

In addition to the structural and optical properties of the coatingsproduced with the apparatus, systems and methods of this invention, thedry processes of this invention are more environmentally friendly andcomparatively less hazardous than conventional techniques because theprocesses of this invention do not produce waste solutions that must bedisposed of following the coating processes. In addition, the methods ofthis invention do not require the incorporation of catalytic ions suchas palladium or tin ions that are necessary elements in electrochemicalwet chemical methods. The use of such ions may disadvantageously preventthe subsequent use of the manufactured pigments in various consumerproducts.

Furthermore, the methods and systems of this invention require no highheating or any pyrolysis. Instead, the coating is deposited according tothe methods of this invention by a dry, low temperature process ratherthan a wet chemical process or a pyrolytic process. More precisely,“dry” in the context of this invention stands for the non-reliance onsolutions by the deposition methods. Instead, the dry vacuum methods ofthis invention are implemented under conditions that are typical ofphysical vapor deposition techniques. The dry vacuum process of theinvention can be carried out at a temperature of less than about 200° C.if desired. In one preferred method, the dry vacuum process is carriedout at a near ambient temperature (e.g., about 20-60 C.). Alternatively,the dry vacuum process can be carried out at a temperature of about 200°C. or greater.

The coatings deposited according to this invention are highly adherent,hard films that do not rub-off, unlike prior coatings such as carboncoatings that are deposited by pyrolytic processes. Organometalliccompounds are more expensive than the materials used in physicaldeposition methods, and some of these compounds are toxic, a propertythat requires investment in equipment for handling the compoundsthemselves and for monitoring the processes in which they are used.

Color Measurement

The chromatic properties of the coated particles produced according tothe invention are quantitatively described with reference to colormeasurement standards that are briefly summarized as follows.

In order to quantify the perceived color of a particular object, it isuseful to invoke the XYZ tristimulus color coordinate system developedby the Commission Internationale de l'Éclairage (CIE), which is now usedas a standard in the industry in order to precisely describe colorvalues. In this system, colors can be related completely and accuratelythrough the variables X, Y, and Z, which are determined mathematicallyas the integrals of three distribution functions covering the visiblespectrum, which ranges from about 380 nm to about 770 μm, with thereflectance or transmittance curve and the energy distribution of thelight source. The variables x, y, and z, which are normalized values ofX, Y, and Z, respectively, are known in the art as the chromaticitycoordinates, and are routinely used in the industry to quantify aspectsof color such as purity, hue, and brightness.

Another color coordinate system developed by CIE defines colorcharacteristics which account for the dependence of color sensitivity ofthe eye on viewing angle in terms of X₁₀Y₁₀Z₁₀ tristimulus values. Thesevalues may be used for viewing angles greater than 4° (and are exact fora viewing angle of 10°), while the values X, Y, and Z are reserved forviewing angles specified for a 4° angle or less.

The parameters X, Y, and Z are defined by the following equations:

X=KS( )x′( )R( )d

Y=KS( )y′( )R( )d

Z=KS( )z′( )R( )d

where

K=100/(S( )y′( )d)

S( ) is the relative spectral power distribution of the illuminant;

x′( ), y′( ), and z′( ) are the color matching functions for a specifiedangle; and

R( ) is the spectral reflectance of the specimen.

The chromaticity coordinates, x, y, and z can be calculated from the X,Y, Z tristimulus values through the following formulae:

x=X/(X+Y+Z)

y=Y/(X+Y+Z)

z=Z/(X+Y+Z)=1−x−y.

From the x, y, z chromaticity coordinates, a useful diagram known as the“chromaticity diagram” can be plotted, wherein the loci of x and yvalues correspond to all real colors; which in conjunction with thehuman eye response function and the third dimension of brightness (whichmay be conveniently plotted on an axis perpendicular to the chromaticityplane), can be used to completely describe all aspects of perceivedcolor. This system of color description is particularly useful when aquantitative comparison of color attributes is required.

The chromaticity plane may be described in a variety of ways; however, astandard in the industry is known as the L*a*b* color space defined byCIE (hereinafter referred to as the “CIELab space”). In this colorspace, L* indicates lightness and a* and b* are the chromaticitycoordinates. In an L*a*b* chromaticity diagram, the a* axis isperpendicular to the b* axis, with increasingly positive values of a*signifying deepening chroma of red and increasingly negative values ofa* signify deepening chroma of green. Along the b* axis, increasinglypositive values of b* signify deepening chroma of yellow, whereasincreasingly negative values of b* indicate deepening chroma of blue.The L* axis indicating lightness is perpendicular to the plane of the a*and b* axes. Colors with no chroma always have the value a*=b*=0. The L*axis along with the a* and b* axes provide for a complete description ofthe color attributes of an object.

The L*a*b*color system allows for a comparison of the color differencesbetween two measurements through a metric, namely E, which indicates thechange in color as measured in the L*a*b* color space. The numericalvalue for E is calculated through the following equation using themeasured L*a*b* values:

E=[(L*)²+(a*)²+(b*)²]^(1/2)

where the symbol denotes a difference in measurements taken, forexample, at two different angles (e.g., 0° incidence and 45° incidence),or a difference in measurements taken for a reference standard and asample.

In general, three items are needed to specify our perception of a givenbeam of light. The L*a*b* set of coordinates is one of such sets ofthree items. Another set incorporates lightness, L*, but instead of thecoordinates a* and b*, it uses the coordinates C* and h, that stand forchroma and hue, respectively. Chroma measures color saturation.Increasing fading corresponds to lower saturation. Hue corresponds withthe dominant saturated color.

Color differences can also be expressed as a function of differences inlightness, chroma and hue by the expression:

E=[(L*)²+(C*)²+(H*)²]^(1/2),

where C* stands for chroma and H* for change in metric hue. The metrichue, h, is defined by

h=arctan (b*/a*)

and the chroma, C*, is defined by

C*=[a* ² +b* ²]^(1/2).

The widely used CIELab color space is adequate for describing pigmentsof a single color. However, color-shifting pigments such as lightinterference pigments represent a significant challenge in colormeasurement. To quantify the dramatic hue shift and chroma of thesecolorants, metrologists at Flex Products, Inc., developed a new colormeasurement metric known as Dynamic Color Area™ (hereinafter “DCA™”).See Flex Products Technical Bulletin No. TB-02-98, which is herebyincorporated by reference herein in its entirety. Measurements tocompute the DCA™ metric are taken at a viewing geometry known as nearspecular multi-angle geometry, where the aspecular view angle is fixedrelative to the corresponding specular angle. The fixed aspecular angleis maintained at all selected angles of illumination. It is measuredusing a goniospectrophotometer, which is an instrument that allows forthe configuration of nearly 300 distinct measurement geometries. Inaddition, the DCA™ metric can also be applied to other multi-anglemeasurement geometries. Calculating the DCA™ metric under two differentgeometries allows for a comparison of pigment appearance under twosimulated viewing environments.

To generate the DCA™ diagram using the aspecular angle geometry, aseries of readings are taken with a goniospectrophotometer at anglesfrom 10° to 60° incidence in 5° increments. These readings are plottedin a CIELab color space. Lines are drawn connecting the plot points andconnecting the 10° and 60° measurements to the achromatic point (a*=0,b*=0), thus defining a function f(a*, b*). The DCA™ metric isrepresented by the area in the a*-b* plane defined by the function f(a*,b*). The larger the area defined by the DCA™ metric for a given pigment,the larger that pigment's color gamut.

More explicitly, the DCA™ metric is described as a defined surfaceintegral

f(a*, b*)db*da*

where the integrations are performed between the lower and upper limitsb₁, b₂, respectively, for b*, and the lower and upper limits a₁, a₂,respectively, for a*. This double integral provides an area in the a*-b*plane of the CIELab space. This area, and thus the DCA™ metric, ismeasured in square CIE units.

Experiments in the context of this invention were performed withcommercially available TiO₂-coated interference mica. The TiO₂-coatedmica having the colors of Super Green Pearl, Violet Pearl and Gold Pearlunder the tradename MasterTint® was obtained from DuPont. TiO₂-coatedmica under the tradename Iriodin® was also obtained from E. Merck(Darmstadt, Germany). Samples of Iriodin® 221 Blue, Iriodin® 289 FlashInterference Blue, and Iriodin® 299 Flash Interference Green were used.A sample under the Mearlin tradename labelled Super Red Mearlin Lusterpigment was obtained from the Engelhard Corporation (Ossining, N.Y.).Similar interference mica can be obtained from Kemira Oy (Pori,Finland), under the tradename Flonac. The substrate material was placedin a coating apparatus according to this invention, for example, avibrating bed in a vacuum chamber. Other experiments used a rotating oran oscillatory drum coater, electromagnetic conveyors, or free fallingcoating towers.

EXAMPLES

The following examples are given to illustrate the present invention,and are not intended to limit the scope of the invention. The examplesutilize the L*a*b* or the L*C*h color space as described above in orderto evaluate color shifting properties of the coatings of this invention.

Example 1

Gold Pearl interference pigment was first washed in acetone and dried inan air oven. The dried pigment was then placed in a cooled dish placedin a vacuum chamber pumped to a pressure of about 1 10⁻⁴ Torr andsubjected to DC magnetron coating of chromium in an Ar pressure of about2.5 10⁻³ Torr.

Example 2

Super Green Pearl pigment was similarly washed and dried as described inExample 1. It too was exposed to sputter deposition of chromium whilebeing subjected to vibrational movement.

Example 3

Violet Pearl pigment was treated as described in Example 1. It was alsosputter coated with chromium.

Example 4

Iriodin® 221 Blue pigment was coated with chromium in a barrel vacuumcoater equipped with two chromium magnetron sources measuring 5″×15″ insize. The magnetrons were run at about 3 A at 3 mTorr Ar for between 6and 20 min depending on the color enhancement required. A mass of about25-50 g of powder was processed without any pre-treatment, washing ordrying.

Example 5

289 Flash Interference Blue pigment was coated with Cr by the sameprocess as described in Example 4.

Example 6

299 Flash Interference Green pigment was coated with Cr by the sameprocess as described in Example 4.

Example 7

Super Red Mearlin® Luster pigment was coated with Cr by the same processas described in Example 4.

Example 8

The pigments identified in Examples 1-7 were utilized with no additionalcoating as control pigments. Cr-coated pigments according to Examples1-7 and the control pigments were sprayed onto white and onto blackcoated paper panels to produce test samples. The sprayed materialsincluded 25% by weight of pigment loading in an acrylic-melamine binder.The dried sprayed material was about 1 mil thick. The microscopiccharacteristics and colors of the control and Cr-coated samples arediscussed below.

Structural Characteristics

FIGS. 6A-6B, and 7A-7C show scanning electron microscopic pictures ofsprayed control pigments and Cr-coated pigments according to thisinvention. FIGS. 6A and 7A show scanning electron microscopic picturesof the surfaces of control Gold Pearl pigment at 50000× and controlSuper Green Pearl pigment at 75000×, respectively. FIGS. 6B and 7B show,respectively, scanning electron microscopic pictures of the surface at50000× of the chromium-coated Gold Pearl pigment in Example 1, and ofthe surface at 75000× of the chromium-coated Super Green Pearl inExample 2. In addition, FIG. 7C shows a scanning electron microscopicpicture of the surface at 100000× of Super Green Pearl pigment that wascoated with Cr as described in Example 2.

Comparison of the picture shown in FIG. 6A with that shown in FIG. 6Breveals that the coating with Cr according to this invention has simplyreplicated the underlying structure of the TiO₂ at 50000× magnification.Similarly, comparison of the picture shown in FIG. 7A with that shown inFIG. 7B reveals that, even at the 75000× magnification level, thecoating with Cr according to this invention has simply replicated theunderlying structure of the TiO₂. FIG. 7C shows that no islands orrod-like particles of Cr are visible at the 100000× magnification levelof the Cr-coated pigment according to this invention. Instead, thestructure at this level of magnification still appears as that of theunderlying TiO₂ layer. Thus, a snow-ball structure of TiO₂ clusters isobserved in all the scanning electron microscopy pictures of the controland Cr-coated pigments according to this invention.

In contrast, the photograph shown in U.S. Pat. No. 5,116,664 (the “'664patent”), where the metal has been deposited by electroless methods,reveals the existence of finely divided rod-like particles (see alsocol. 6, line 16 in the '664 patent). The magnification at which thephotograph in the '664 patent is shown is 72000×, whereas not even thephotograph shown in FIG. 7C, taken at 100000×, for the Cr-coated pigmentaccording to this invention shows the presence of any type of formationother than the uniform coating of the TiO₂ layer. In particular, noscanning electron microscopic picture of the chromium-coated surfaceaccording to this invention shows any rod-like formation or island.Instead, the pictures in FIGS. 6B, 7B, and 7C show a smooth replicationof the structure of the TiO₂ layer by the coating of chromium.

Optical Properties

Compared to the control samples, the chromium coated pigments in somesamples exhibited a higher chroma, a higher dynamic color shift, and ahigher hiding power. Hue changes, i.e., color changes, were also noted.

The higher hiding power was readily seen by comparing spray out sampleson white paper panels. Under visual inspection, the control samples onthe white paper background showed a slight reflection in color at nearnormal angle, but at a glancing angle the white paper was readilyvisible. On black paper, the control showed little difference inreflection at normal versus glancing angle, i.e., the colors werepractically the same. In contrast, the chromium-coated pigment showedlittle, if any, difference in color whether it was sprayed over a blackor white background. The pigment itself was also notably different. Thecontrol pigment was whitish in color whereas the Cr-coated pigment wascolored.

Upon visual inspection, the control samples on a white background onlyshowed reflected color at near normal incidence. At higher angles, onlythe mass tone of the white background is seen. In contrast, the treatedCr-coated interference mica showed the color of the pigment at allangles. This observation implies a much improved hiding power (hidingthe background color) over the control samples.

Table 1 shows the difference between the color parameters for thecontrol pigments on white and on black paper panels versus the Cr-coatedpigments also on white and on black paper panels for the samples inExamples 1-3. The L*a*b* coordinates were measured at 10° incidence witha D₆₅ illuminant (CIE illuminant with a color temperature of 6504 K)with a Data Color 600 color integrating measuring instrument. DCA™calculations were based on color measurements using off-gloss (i.e.,specular) geometry on a Zeiss GK 311M spectrophotometer. As describedhereinabove, DCA™ is a measure of the color gamut available as the angleof viewing is changed.

TABLE 1 Color Properties of Coated and Un-Coated Interference Mica Back-Sample ground DCA L* a* b* C* h Gold Pearl White 49.4 90.6 −2.3 15.215.4 98.6 Gold Pearl + White 128.9 71.0 1.4 21.3 21.3 86.0 Cr Gold PearlBlack 89.1 76.8 −1.0 24.6 24.9 92.2 Gold Pearl + Black 130.9 66.5 1.7225.5 25.6 86.2 Cr Super Green White 223.8 89.2 −5.17 13.3 14.3 111.2Super Green + White 487.3 67.7 −11.8 14.6 18.8 129.0 Cr Super GreenBlack 380.6 75.1 −15.3 10.0 18.25 146.8 Super Green + Black 534.9 65.1−14.7 15.0 21.0 134.5 Cr Violet Pearl White 232.2 91.4 −0.77 5.74 5.7997.7 Violet Pearl + White 523.8 50.9 8.1 −16.0 17.9 296.6 Cr VioletPearl Black 982.5 47.5 20.0 −27.7 34.2 305.8 Violet Pearl + Black 716.943.9 10.7 −24.0 26.3 294.1 Cr

The DCA™ values in Table 1 for the Cr-coated pigments are greater thanthe corresponding values for the control samples by a factor in therange of approximately 1.4-2.6. This means that the available colorgamut for the Cr-coated pigments has been increased by the same factor.As shown in Table 1, the DCA™ value for the Violet Pearl+Cr on a blackbackground is lower than the corresponding value for the uncoated VioletPearl (control). This observation is explained in terms of an excess ofdeposited chromium, which results in lower chroma because it moves thecolor saturation towards the achromatic point at (a*, b*)=(0, 0), theorigin. This lower chroma decreases the DCA™ value. The chroma for theViolet Pearl+Cr is still higher than the chroma for the control with nochromium on the white background because the chroma for the control on awhite background is initially very low. Generally, as chromium is beingadded, the chroma and DCA™ values will increase, but with additionalchromium deposition the chroma and DCA™ values will ultimately decreaseas the pigment behaves more like chromium powder. The intensification ofchroma with the added layer of chromium is due to an increase inabsorption and interference effects.

Example 9

Further color characterization using D₆₅ illumination was performed witha Zeiss spectrophotometer to show the color at various viewing angles;the measurements were also taken just off-gloss conditions. FIG. 8 is aplot in a*b* color space that shows the hue and chroma changes for thethree DuPont pigments in Examples 1-3 as the viewing angles change. Forall the pigments whose chroma and hue are plotted in FIG. 8, theCr-coated pigment as sprayed with the binder on white background hashigher chroma than the corresponding control sample as similarly sprayedwith the binder on white background. This is shown in FIG. 8 by thelocation of the chroma point loci for the Cr-coated pigments and thosefor the corresponding control samples. The chroma point loci for theCr-coated pigments are farther from the center of the a*b* axis systemthan point loci for the corresponding control samples. This is alsosatisfied for the chroma point loci when the background is black for thepigments in Examples 1 and 2.

More specifically, the loci of chroma points 802 and 804 in FIG. 8correspond to the Gold Pearl interference pigment in Example 1 on whitebackground in the form of control sample and with Cr-coating accordingto this invention, respectively. Similarly, the loci of chroma points812, 814 and 822, 824 correspond to the pigments Super Green Pearl inExample 2 and Violet Pearl in Example 3, respectively. The loci 812 and822 are for the control samples on a white background and the loci 814and 824 are for the Cr-coated pigments also on white background. Thepair of loci chroma points 812, 814 is for the pigment in Example 2 andthe pair of chroma points 822, 824 is for the pigment in Example 3. Thesets of loci of chroma points 804, 814 and 824 for the Cr-coatedpigments on white background are farther from the origin of the a*b*coordinate system than the respective counterparts 802, 812 and 822 forthe control samples on white background. In addition, the sets of lociof chroma points 803 and 813 for the Cr-coated pigments on blackbackground in Examples 1 and 2 are also farther from the origin of thea*b* coordinate system than the respective counterparts 801 and 811 forthe control samples on black background. These observations areconsistent with the changes in chroma values (C* values) given in Table1 for one measurement at 10°.

Example 10

Color measurements of the spray out paper panels were made on both thewhite and black backgrounds for both Cr-coated and control TiO₂-coatedinterference mica with a Zeiss color measuring instrument set-up formulti-angle geometry. Data obtained with these measurements are given inTables 2-29. Samples were illuminated at 45° and 130° (second column ineach one of Tables 2-29), and measured at five angles relative to thegloss angle using D₆₅ illumination. These angles were 15°, 25°, 45°, 65°and 105° (given in the fourth column in each one of Tables 2-29), andnumbered with ordinal numbers in the first column of each one of Tables2-29. The entries in each of the second columns in these tables are theangles of illumination. For each angle of illumination, the angle ofdetection is listed in the third column under the heading “View”. Thegloss angle is the angle for which the angle of incidence is equal tothe angle of reflection, and the difference between the gloss angle andthe angle of detection is the angle listed in the fourth column underthe heading “Diff.” for each measurement. The fifth column in each tableunder the heading “Filt.” provides the neutral density filter setting,where unity means that no filter was used. These Tables providenumerical values for the CIE color coordinates a*, b*, L*, C*, and h forthe different control and Cr-coated pigments on white and on blackbackgrounds.

TABLE 2 Sample: Control Violet Pearl in Example 3 on white background.Points (a*, b*) in this Table correspond to filled diamonds in FIG. 9. NIllum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 64.04 71.4358.18 87.69 −8.25 15.71 17.75 117.71 2 45 70 65 1 64.74 72.07 56.2788.00 −8.00 18.05 19.74 113.91 3 45 90 45 1 69.25 75.39 63.20 89.57−4.77 14.40 15.17 108.33 4 45 110 25 1 90.05 90.29 101.01 96.12 8.22−2.68 8.65 341.93 5 45 120 15 1 112.77 105.66 141.13 102.15 20.51 −15.4025.65 323.11

TABLE 3 Sample: Control Violet Pearl in Example 3 on black background.Points (a*, b*) in this Table correspond to triangles in FIG. 9. N IllumView Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 5.41 5.22 8.7327.36 5.60 −11.88 13.13 295.21 2 45 70 65 1 6.05 5.56 10.54 28.28 8.91−15.92 18.25 299.22 3 45 90 45 1 10.30 8.73 18.60 35.46 16.77 −22.7928.30 306.34 4 45 110 25 1 31.63 23.70 57.78 55.79 37.34 −38.93 53.94313.81 5 45 120 15 1 57.92 41.42 103.57 70.47 51.57 −48.55 70.83 316.72

TABLE 4 Sample: Cr-coated Violet Pearl in Example 3 on white background.Points (a*, b*) in this Table correspond to filled squares in FIG. 9. NIllum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 6.68 6.966.23 31.71 0.83 4.83 4.90 80.29 2 45 70 65 1 8.31 8.58 8.63 35.17 1.581.92 2.49 50.49 3 45 90 45 1 11.62 11.41 15.43 40.26 5.85 −7.78 9.74306.95 4 45 110 25 1 27.63 24.64 47.96 56.72 18.05 −27.52 32.91 303.26 545 120 15 1 48.76 41.67 89.97 70.65 27.12 −39.18 47.65 304.69

TABLE 5 Sample: Cr-coated Violet Pearl in Example 3 on black background.Points (a*, b*) in this Table correspond to crosses in FIG. 9. N IllumView Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 1.71 1.65 2.9413.55 3.65 −9.35 10.03 291.30 2 45 70 65 1 2.72 2.56 5.06 18.17 5.82−13.31 14.53 293.62 3 45 90 45 1 5.90 5.37 11.55 27.76 9.54 −19.69 21.88295.86 4 45 110 25 1 23.08 19.44 46.98 51.20 22.53 −35.99 42.46 302.05 545 120 15 1 47.23 38.27 96.72 68.22 33.35 −47.97 58.42 304.81

TABLE 6 Sample: Control Gold Pearl in Example 1 on white background.Points (a*, b*) in this Table correspond to filled diamonds in FIG. 10.N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 46.4949.82 49.52 75.96 −2.09 4.02 4.53 117.46 2 45 70 65 1 45.47 48.94 50.7075.41 −2.64 1.85 3.22 144.94 3 45 90 45 1 57.64 61.87 57.03 82.84 −2.478.43 8.79 106.31 4 45 110 25 1 114.22 122.06 83.71 107.97 −2.33 29.6529.74 94.49 5 45 120 15 1 180.92 192.41 113.90 128.28 −1.71 44.76 44.8092.19

TABLE 7 Sample: Control Gold Pearl in Example 1 on black background.Points (a*, b*) in this Table correspond to triangles in FIG. 10. NIllum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 17.60 18.9117.36 50.59 −1.77 5.84 6.10 106.86 2 45 70 65 1 21.13 22.59 18.50 54.65−1.37 10.51 10.60 97.43 3 45 90 45 1 35.80 38.10 25.57 68.09 −1.08 21.0121.03 92.94 4 45 110 25 1 90.79 96.71 51.95 98.71 −1.62 40.76 40.7992.27 5 45 120 15 1 145.09 154.20 77.74 118.02 −1.47 51.45 51.47 91.63

TABLE 8 Sample: Cr-coated Gold Pearl in Example 1 on white background.Points (a*, b*) in this Table correspond to squares in FIG. 10. N IllumView Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 11.74 12.28 12.5641.66 0.67 1.59 1.73 67.04 2 45 70 65 1 13.93 14.60 14.05 45.08 0.593.75 3.80 81.12 3 45 90 45 1 22.76 23.83 18.35 55.91 0.77 12.99 13.0186.60 4 45 110 25 1 70.08 73.27 40.14 88.58 1.31 36.22 36.24 87.92 5 45120 15 1 138.59 144.49 70.70 115.14 2.19 52.09 52.14 87.59

TABLE 9 Sample: Cr-coated Gold Pearl in Example 1 on black background.Points (a*, b*) in this Table correspond to crosses in FIG. 10. N IllumView Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 5.52 5.81 5.6328.92 0.22 2.59 2.60 85.07 2 45 70 65 1 8.28 8.65 6.83 35.30 0.76 8.618.64 84.97 3 45 90 45 1 17.33 18.06 11.24 49.57 1.13 18.79 18.83 86.57 445 110 25 1 65.89 68.77 34.08 86.39 1.56 40.09 40.12 87.77 5 45 120 15 1136.62 142.66 65.35 114.59 1.89 55.64 55.67 88.06

TABLE 10 Sample: Control Super Green Pearl in Example 2 on whitebackground. Points (a*, b*) in this Table correspond to filled diamondsin FIG. 11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −1051 51.50 53.66 44.77 78.27 1.65 13.10 13.20 82.81 2 45 70 65 1 50.8752.89 45.79 77.81 1.93 11.18 11.35 80.21 3 45 90 45 1 61.31 65.59 55.3784.79 −2.05 13.37 13.53 98.71 4 45 110 25 1 96087 109.82 90.76 103.68−12.26 17.22 21.14 125.44 5 45 120 15 1 126.91 148.45 126.98 116.33−19.33 16.63 25.50 139.31

TABLE 11 Sample: Control Super Green Pearl in Example 2 on blackbackground. Points (a*, b*) in this Table correspond to triangles inFIG. 11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 116.33 19.30 21.82 51.03 −10.71 −2.03 10.90 190.73 2 45 70 65 1 20.1723.69 23.53 55.78 −10.91 3.16 11.36 163.82 3 45 90 45 1 31.55 37.4233.25 67.59 −13.80 8.80 16.37 147.49 4 45 110 25 1 68.29 83.30 71.0893.14 −22.26 13.86 26.22 148.10 5 45 120 15 1 100.44 124.95 110.37108.94 −28.83 13.55 31.85 154.83

TABLE 12 Sample: Cr-coated Super Green Pearl in Example 2 on whitebackground. Points (a*, b*) in this Table correspond to squares in FIG.11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 8.839.35 8.78 36.65 −0.32 3.96 3.97 94.67 2 45 70 65 1 11.65 12.64 10.9942.21 −2.34 6.80 7.19 109.03 3 45 90 45 1 19.40 22.09 17.22 54.12 −7.6112.22 14.39 121.90 4 45 110 25 1 53.75 65.16 49.14 84.57 −19.65 19.2527.51 135.59 5 45 120 15 1 94.25 117.89 93.15 106.54 −29.17 20.51 35.66144.89

TABLE 13 Sample: Cr-coated Super Green Pearl in Example 2 on blackbackground. Points (a*, b*) in this Table correspond to crosses in FIG.11. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 130 155 −105 1 4.705.54 5.85 28.21 −6.85 0.42 6.87 176.51 2 45 70 65 1 7.68 9.10 7.84 36.17−8.54 6.37 10.65 143.30 3 45 90 45 1 15.60 18.66 14.25 50.28 −11.7012.26 16.95 133.65 4 45 110 25 1 49.73 61.69 46.12 82.75 −22.43 19.3529.62 139.22 5 45 120 15 1 87.73 110.80 87.67 104.04 −30.16 20.01 36.19146.44

TABLE 14 Sample: Control Super Red Merlin Luster in Example 7 on whitebackground. Points (a*, b*) in this Table correspond to filled diamondsin FIG. 12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 158.75 67.62 59.57 85.82 −12.58 11.19 16.84 138.35 2 45 90 45 1 67.8875.06 66.88 89.42 −7.11 10.94 13.05 123.02 3 45 110 25 1 110.03 107.50101.56 102.83 13.25 8.54 15.76 32.80 4 45 120 15 1 161.72 147.23 139.02115.96 28.60 9.52 30.14 18.41 5 130 155 −105 1 57.08 64.28 58.83 84.11−9.32 8.93 12.91 136.21

TABLE 15 Sample: Control Super Red Merlin Luster in Example 7 on blackbackground. Points (a*, b*) in this Table correspond to squares in FIG.12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 1 13.3212.39 14.23 41.83 10.66 −2.27 10.90 347.99 2 45 90 45 1 21.45 18.7621.45 50.41 18.45 −2.43 18.60 352.49 3 45 110 25 1 56.05 46.02 48.5573.56 33.63 0.88 33.64 1.50 4 45 120 15 1 93.99 76.13 74.93 89.92 42.015.20 42.33 7.06 5 130 155 −105 1 12.41 12.19 12.89 41.51 5.98 0.49 6.004.69

TABLE 16 Sample: Cr-coated Super Red Merlin Luster in Example 7 on whitebackground. Points (a*, b*) in this Table correspond to triangles inFIG. 12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 1 8.988.32 9.56 34.63 9.66 −2.02 9.87 348.19 2 45 90 45 1 17.49 15.40 17.7646.18 16.61 −2.58 16.81 351.17 3 45 110 25 1 48.18 40.98 43.30 70.1627.61 0.78 27.63 1.61 4 45 120 15 1 77.12 65.35 65.13 84.66 32.84 4.2433.11 7.35 5 130 155 −105 1 5.26 5.18 5.63 27.25 4.32 0.30 4.34 355.98

TABLE 17 Sample: Cr-coated Super Red Merlin Luster in Example 7 on blackbackground. Points (a*, b*) in this Table correspond to crosses in FIG.12. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 1 7.38 6.838.07 31.41 9.15 −2.68 9.53 343.70 2 45 90 45 1 14.03 12.41 14.25 41.8615.07 −2.26 15.24 351.47 3 45 110 25 1 39.74 33.77 36.38 64.78 26.01−0.17 26.01 359.63 4 45 120 15 1 69.38 58.53 59.11 81.03 32.32 3.3632.49 5.94 5 130 155 −105 1 5.21 5.00 5.67 26.72 5.90 −1.40 6.06 346.65

TABLE 18 Sample: Control Merck Iriodin ® 221 Blue in Example 4 on whitebackground. Points (a*, b*) in this Table correspond to filled diamondsin FIG. 13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 169.83 72.82 54.97 88.36 1.70 19.92 20.00 85.11 2 45 90 45 1 75.52 79.4370.94 91.43 0.44 11.01 11.02 87.70 3 45 110 25 1 88.45 94.28 112.6097.75 −1.71 −7.10 7.31 256.43 4 45 120 15 1 95.35 101.31 137.08 100.50−1.23 −16.12 16.16 265.64 5 130 155 −105 1 63.75 67.23 49.57 85.62 0.0220.62 20.62 89.95

TABLE 19 Sample: Control Merck Iriodin ® 221 Blue in Example 4 on blackbackground. Points (a*, b*) in this Table correspond to squares in FIG.13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 1 18.5920.53 32.40 52.43 −4.48 −16.17 16.78 254.52 2 45 90 45 1 22.40 25.2842.96 57.35 −7.04 −20.93 22.08 251.40 3 45 110 25 1 35.00 39.58 81.0969.17 −8.44 −35.30 36.30 256.56 4 45 120 15 1 45.35 50.24 115.12 76.22−6.46 −45.72 46.18 261.96 5 130 155 −105 1 19.02 20.31 30.82 52.19 −1.20−14.38 14.43 265.24

TABLE 20 Sample: Cr-coated Merck Iriodin ® 221 Blue in Example 4 onwhite background. Points (a*, b*) in this Table correspond to trianglesin FIG. 13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 19.23 9.95 14.17 37.74 −1.64 −9.17 9.31 259.84 2 45 90 45 1 14.19 15.6425.72 46.50 −3.94 −16.46 16.92 256.54 3 45 110 25 1 30.97 33.98 71.2664.94 −4.56 −34.91 35.21 262.56 4 45 120 15 1 45.84 49.26 113.80 75.61−2.45 −45.99 46.05 266.95 5 130 155 −105 1 7.37 7.69 10.48 33.34 0.72−7.04 7.08 275.83

TABLE 21 Sample: Cr-coated Merck Iriodin ® 221 Blue in Example 4 onblack background. Points (a*, b*) in this Table correspond to crosses inFIG. 13. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 1 7.498.31 13.71 34.63 −3.67 −13.43 13.92 254.71 2 45 90 45 1 11.94 13.4224.41 43.38 −5.36 −19.68 20.40 254.76 3 45 110 25 1 27.05 29.99 64.5161.64 −5.49 −34.91 35.34 261.06 4 45 120 15 1 40.30 43.59 102.10 71.95−3.16 −45.05 45.16 265.99 5 130 155 −105 1 6.05 6.44 10.29 30.49 −0.62−11.36 11.38 266.85

TABLE 22 Sample: Control Iriodin ® Flash Interference Blue in Example 5on white background. Points (a*, b*) in this Table correspond to filleddiamonds in FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 64.02 65.80 47.85 84.90 3.77 21.18 21.51 79.91 2 45 90 45 168.11 70.52 56.17 87.25 2.75 16.85 17.08 80.73 3 45 110 25 1 90.20 97.93110.29 99.19 −4.77 −3.21 5.75 213.93 4 45 120 15 1 128.74 143.80 222.82114.93 −10.68 −29.39 31.27 250.02 5 130 155 −105 1 63.93 67.22 50.2885.61 0.46 19.87 19.88 88.68

TABLE 23 Sample: Control Iriodin ® Flash Interference Blue in Example 5on black background. Points (a*, b*) in this Table correspond to squaresin FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 112.32 13.40 22.27 43.36 −2.63 −16.06 16.27 260.68 2 45 90 45 1 15.8917.80 29.89 49.25 −5.58 −18.10 18.94 252.88 3 45 110 25 1 34.88 41.1276.30 70.26 −13.54 −29.76 32.70 245.53 4 45 120 15 1 70.68 83.41 179.3493.19 −17.29 −49.06 52.01 250.58 5 130 155 −105 1 12.61 13.33 22.6143.26 −0.24 −16.81 16.82 269.17

TABLE 24 Sample: Cr-coated Iriodin ® Flash Interference Blue in Example5 on white background. Points (a*, b*) in this Table correspond totriangles in FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 5.30 5.70 8.42 28.64 −1.20 −8.64 8.72 262.12 2 45 90 45 1 8.939.88 15.17 37.62 −3.64 −11.73 12.28 252.75 3 45 110 25 1 29.16 32.7855.52 63.98 −7.23 −22.64 23.77 252.28 4 45 120 15 1 70.04 77.93 144.1890.75 −8.14 −36.62 37.51 257.47 5 130 155 −105 1 3.58 3.73 5.51 22.75−0.65 −7.50 7.53 274.96

TABLE 25 Sample: Cr-coated Iriodin ® Flash Interference Blue in Example5 on black background. Points (a*, b*) in this Table correspond tocrosses in FIG. 14. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 7065 1 4.54 4.94 7.85 26.58 −1.95 −10.22 10.40 259.17 2 45 90 45 1 7.728.59 13.73 35.18 −3.92 −12.52 13.12 252.61 3 45 110 25 1 23.37 26.2244.38 58.24 −6.52 −20.98 21.97 252.75 4 45 120 15 1 52.35 58.40 105.9680.96 −7.75 −31.96 32.89 256.37 5 130 155 −105 1 3.31 3.49 5.81 21.890.02 −10.31 10.31 270.13

TABLE 26 Sample: Control Iriodin ® Flash Interference Green in Example 6on white background. Points (a*, b*) in this Table correspond to filleddiamonds in FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 66.46 68.11 69.73 86.06 4.23 2.75 5.05 33.02 2 45 90 45 1 69.3871.66 72.99 87.81 3.12 3.11 4.40 44.86 3 45 110 25 1 92.14 100.31 93.32100.12 −5.26 9.32 10.70 119.43 4 45 120 15 1 154.64 180.40 150.44 125.21−20.11 19.65 28.12 135.66 5 130 155 −105 1 67.48 69.75 67.54 86.88 2.985.99 6.70 63.55

TABLE 27 Sample: Control Iriodin ® Flash Interference Green in Example 6on black background. Points (a*, b*) in this Table correspond to squaresin FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 70 65 16.45 7.17 11.38 32.18 −3.53 −11.59 12.11 253.06 2 45 90 45 1 10.59 12.3515.21 41.76 −8.15 −4.69 9.40 209.90 3 45 110 25 1 37.53 46.25 39.5873.71 −19.55 11.24 22.55 150.10 4 45 120 15 1 87.38 109.71 85.80 103.64−29.10 20.66 35.69 144.63 5 130 155 −105 1 5.46 5.98 10.53 29.35 −2.40−14.04 14.24 260.28

TABLE 28 Sample: Cr-coated Iriodin ® Flash Interference Green in Example6 on white background. Points (a*, b*) in this Table correspond totriangles in FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 4570 65 1 8.36 8.97 11.32 35.94 −1.29 −4.95 5.12 255.42 2 45 90 45 1 12.8614.25 15.29 44.60 −4.26 0.03 4.26 179.57 3 45 110 25 1 41.41 48.42 38.9675.09 −13.26 14.38 19.56 132.67 4 45 120 15 1 112.72 136.54 101.05112.69 −25.01 25.86 35.98 134.04 5 130 155 −105 1 6.79 7.24 9.85 32.35−0.80 −6.84 6.89 263.36

TABLE 29 Sample: Cr-coated Iriodin ® Flash Interference Green in Example6 on black background. Points (a*, b*) in this Table correspond tocrosses in FIG. 15. N Illum View Diff. Filt. X Y Z L* a* b* C* h 1 45 7065 1 6.87 7.58 10.27 33.09 −3.11 −6.85 7.52 245.57 2 45 90 45 1 10.6212.01 13.60 41.24 −5.65 −1.76 5.92 197.29 3 45 110 25 1 32.85 38.6532.04 68.50 −13.03 12.03 17.73 137.30 4 45 120 15 1 84.12 101.35 76.18100.52 −21.78 22.50 31.32 134.07 5 130 155 −105 1 5.59 6.13 9.24 29.74−2.61 −9.44 9.79 254.53

FIGS. 9-15 show the plots of the data given in Tables 2-29 for therespective pigments: Violet Pearl, Gold Pearl, Super Green Pearl, SuperRed Mearlin Luster, Merck Iriodin® 221 Blue, Iriodin®289 FlashInterference Blue, and Iriodin® 299 Flash Interference Green. The colorcharacteristics are plotted in the a*b* space for the correspondingcontrol sample on white and on black backgrounds and for the Cr-coatedpigment according to this invention on white and on black backgrounds.

FIGS. 9-15 invariably show in all cases that the Cr-coated pigmentsaccording to this invention gave nearly the same color trajectory onboth the white and black backgrounds whereas the control samples gavewidely different color trajectories. This means that the Cr-coatedpigments according to this invention will give paints a more constantcolor when painted over varying colored backgrounds. One of thepractical consequences of this new attribute is that it allows a paintshop more freedom in repairs, especially when the paint is coveringdifferent colored bases.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing described. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A method of forming a pigment composition,comprising: placing an inorganic powdered substrate material in a vacuumchamber containing one or more coating material vaporization sources;generating a coating material vapor from the one or more coatingmaterial vaporization sources in a dry vacuum process; exposing thepowdered substrate material to the coating material vapor in asubstantially uniform manner; and forming a coalescence film of one ormore layers of coating material on the powdered substrate material thatsubstantially replicates a surface microstructure of the powderedsubstrate material.
 2. The method of claim 1, wherein the powderedsubstrate material comprises a silicatic material.
 3. The method ofclaim 1, wherein the powdered substrate material is selected from thegroup consisting of mica flakes, glass flakes, talc, boron nitride, andcombinations thereof.
 4. The method of claim 1, wherein the powderedsubstrate material comprises a silicatic material precoated with a highrefractive index dielectric material.
 5. The method of claim 4, whereinthe high refractive index dielectric material is selected from the groupconsisting of titanium dioxide, zirconium oxide, tin oxide, iron oxide,zinc oxide, tantalum pentoxide, magnesium oxide, tungsten trioxide,carbon, and combinations thereof.
 6. The method of claim 1, wherein thepowdered substrate material comprises a TiO₂-coated interference mica.7. The method of claim 1, wherein the coating material is a lightabsorbing material.
 8. The method of claim 1, wherein the coatingmaterial is selected from the group consisting of metals, oxides,sub-oxides, nitrides, oxynitrides, borides, sulfides, carbides, andcombinations thereof.
 9. The method of claim 1, wherein the coatingmaterial comprises an absorber material selected from the groupconsisting of chromium, titanium, palladium, tin, aluminum, silicon,carbon, copper, cobalt, nickel, titanium silicide, hastelloys, monels,inconels, nichromes, stainless steels, and combinations thereof.
 10. Themethod of claim 1, wherein the coalescence film has a thickness fromabout 30 Å to about 150 Å.
 11. The method of claim 1, wherein thecoating material vaporization sources are selected from the groupconsisting of evaporative sources, sputtering sources, electron beamdeposition sources, and arc vapor deposition sources.
 12. The method ofclaim 1, wherein the dry vacuum process is carried out at a temperatureof less than about 200° C.
 13. The method of claim 1, wherein the dryvacuum process is carried out at a temperature of about 200° C. orgreater.
 14. The method of claim 1, wherein the dry vacuum process iscarried out at a near ambient temperature.
 15. The method of claim 1,wherein the dry vacuum process comprises a physical vapor depositionprocess.
 16. A pigment composition, comprising: a powdered substratematerial comprising a plurality of inorganic core particles having anobservable surface microstructure; and a coalescence film of one or morelayers of a light absorbing material substantially surrounding the coreparticles of the substrate material, the coalescence film substantiallyreplicating the surface microstructure of the core particles.
 17. Thepigment composition of claim 16, wherein the powdered substrate materialcomprises a silicatic material.
 18. The pigment composition of claim 16,wherein the powdered substrate material is selected from the groupconsisting of mica flakes, glass flakes, talc, boron nitride, andcombinations thereof.
 19. The pigment composition of claim 16, whereinthe powdered substrate material comprises a silicatic material precoatedwith a high refractive index dielectric material.
 20. The pigmentcomposition of claim 19, wherein the high refractive index dielectricmaterial is selected from the group consisting of titanium dioxide,zirconium oxide, tin oxide, iron oxide, zinc oxide, tantalum pentoxide,magnesium oxide, tungsten trioxide, carbon, and combinations thereof.21. The pigment composition of claim 16, wherein the powdered substratematerial comprises a TiO₂-coated interference mica.
 22. The pigmentcomposition of claim 16, wherein the coalescence film comprises amaterial selected from the group consisting of metals, oxides,sub-oxides, nitrides, oxynitrides, borides, sulfides, carbides, andcombinations thereof.
 23. The pigment composition of claim 16, whereinthe coalescence film comprises a material selected from the groupconsisting of chromium, titanium, palladium, tin, aluminum, silicon,carbon, copper, cobalt, nickel, titanium silicide, hastelloys, monels,inconels, nichromes, stainless steels, and combinations thereof.
 24. Thepigment composition of claim 16, wherein the coalescence film has athickness from about 30 Å to about 150 Å.
 25. A pigment flake,comprising: an inorganic core particle having an observable surfacemicrostructure; and a coalescence film of one or more layers of a lightabsorbing material substantially surrounding the core particle, thecoalescence film substantially replicating the surface microstructure ofthe core particle.
 26. The pigment flake of claim 25, wherein theinorganic core particle comprises a silicatic material.
 27. The pigmentflake of claim 25, wherein the inorganic core particle comprises amaterial selected from the group consisting of mica flake, glass flake,talc, boron nitride, and combinations thereof.
 28. The pigment flake ofclaim 25, wherein the inorganic core particle comprises a silicaticmaterial precoated with a high refractive index dielectric material. 29.The pigment flake of claim 28, wherein the high refractive indexdielectric material is selected from the group consisting of titaniumdioxide, zirconium oxide, tin oxide, iron oxide, zinc oxide, tantalumpentoxide, magnesium oxide, tungsten trioxide, carbon, and combinationsthereof.
 30. The pigment flake of claim 25, wherein the inorganic coreparticle comprises a TiO₂-coated interference mica.
 31. The pigmentflake of claim 25, wherein the coalescence film comprises a materialselected from the group consisting of a metal, an oxide, a sub-oxide, anitride, an oxynitride, a boride, a sulfide, a carbide, and combinationsthereof.
 32. The pigment flake of claim 25, wherein the coalescence filmcomprises a material selected from the group consisting of chromium,titanium, palladium, tin, aluminum, silicon, carbon, copper, cobalt,nickel, titanium silicide, hastelloys, monels, inconels, nichromes,stainless steels, and combinations thereof.
 33. The pigment flake ofclaim 25, wherein the coalescence film comprises alternating layers oftwo different absorber materials.
 34. The pigment flake of claim 33,wherein the alternating layers of two different absorber materials areselected from the group consisting of Ti/C, Pd/C, Zr/C, Nb/C, Al/C,Cu/C, Ti/W, Ti/Nb, Ti/Si, Al/Si, Pd/Cu, Co/Ni, and Cr/Ni.
 35. A pigmentflake, comprising: a glass core particle having an observable surfacemicrostructure; and a coalescence film of one or more layers of a lightabsorbing material comprising aluminum substantially surrounding thecore particle, the coalescence film substantially replicating thesurface microstructure of the core particle.